The serotonin reuptake blocking medications (SSRIs, such as fluoxetine, fluvoxamine and sertraline) have been demonstrated to be efficacious in the treatment of obsessive-compulsive disorder (OCD), but many patients fail to respond to therapy. Treatment-refractory cases are particularly common among the comorbid ASD-OCD group, suggesting that modulation of serotonin alone is not sufficient for symptom relief in this cohort. The hypothesized etiology of childhood-onset OCD suggests that glutamate antagonists, such as riluzole, might reduce the severity of obsessions and compulsions because the drug works upstream from current pharmacotherapies. There has been some preliminary success in the use of riluzole for OCD among both adults and children. An open label trial of riluzole augmentation was conducted in 13 adult patients with treatment-resistant OCD. Concomitant medicines were continued during the trial and Yale-Brown Obsessive Compulsive Scale (Y-BOCS) scores improved significantly over the course of the investigation. Five subjects were categorized as treatment responders (Y-BOCS less than 16, and 35% or greater reduction in baseline score as well as clinical consensus improvement). Four of six pediatric subjects with OCD showed significant improvements after 12 weeks of open-label administration of riluzole; the treatment gains were sustained at one year follow-up with no serious adverse events reported. Compulsions, including simple, repetitive behaviors were improved as much as more complex rituals, suggesting that riluzole might be of benefit for the stereotyped behaviors of autism, as well as for the obsessions and compulsions. Autism spectrum disorders (ASD) are reported to affect as many as 1 in 150 children, with lifelong disabilities affecting social, communication and psychological functioning. With millions of children affected, ASD represents a tremendous public health problem. Compound the ASD symptoms with medical and psychiatric comorbidity, as frequently occurs, and the costs (in both dollars and suffering) are immense. Currently, there are no medications with demonstrated benefits for any of the three core symptoms of autism (social deficits, communication abnormalities and fixated interests/repetitive behaviors). Although some behavioral strategies are reported to be useful for the social and communication spheres, no behavioral interventions have shown consistent benefits for the fixated interests and repetitive behaviors of ASD. However, given the close similarity between these symptoms and the obsessive-compulsive behaviors seen in childhood-onset obsessive-compulsive disorder (OCD), and the frequency with which OCD is present as a comorbidity in ASD, we postulated that medications which reduce OCD symptoms might also improve the repetitive behaviors and fixated interests of ASD. IRB restrictions limited study participants to children and adolescents who had failed to respond to previous therapy with cognitive-behavioral interventions (specifically, exposure with response prevention) and an SSRI. Most participants were taking psychotropic medications at the time of study entry and continued the drugs throughout study participation. Therefore, the trial was limited in its ability to assess safety and efficacy of riluzole for the treatment of obsessive-compulsive symptoms. 60 children and adolescents(ages 7 to 17 years)with OCD completed the 12-weeks double-blind trial. Overall, there were no significant differences between placebo and riluzole for measures of change in OCD or overall symptom severity. Side-effects of riluzole administration were observed, including elevations of liver transaminases. Long-term (1 year) follow-up evaluations revealed that all subjects were improved from baseline, and many had stopped other psychotropic medications in favor of riluzole therapy. However, the lack of between-group differences significantly limits enthusiasm for further investigations of riluzole for childhood-onset OCD.